package leetcode;
/* Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, 
 * with the colors in the order red, white and blue.
 * Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.
 * Note:
 * You are not suppose to use the library's sort function for this problem.
 * Follow up:
 * A rather straight forward solution is a two-pass algorithm using counting sort.
 * First, iterate the array counting number of 0's, 1's, and 2's, then overwrite array with total number of 0's, 
 * then 1's and followed by 2's.
 * Could you come up with an one-pass algorithm using only constant space?
 */
/* one-pass solution
 */
public class SortColors2 {
	public void sortColors(int[] A) {
		if (A == null || A.length == 0 || A.length == 1)
			return;
		int red = 0, blue = A.length - 1, tmp, i = 0;
		// stop looping when current >= blue
		while (i <= blue) {
			// if color is red, move to the front
			if (A[i] == 0) {
				tmp = A[red];
				A[red] = A[i];
				A[i] = tmp;
				red++;
				i++;
				continue;
			}
			// if color is blue, move to the end
			if (A[i] == 2) {
				tmp = A[blue];
				A[blue] = A[i];
				A[i] = tmp;
				blue--;
				continue;
			}
			i++;
		}
	}
}
